Hi, I have what seems to be a exhaust leak around my left spark plug. There is a small amount of carbon soot on my two fins directly down wind of the plug. When I remove the left plug, the threads are discolored with this carbon soot the entire length of the plug. The right side spark plug threads are clean. I also have a slight "popping" sound on the left side when deaccellerating. Any suggestions on reducing the leak and the popping noise? Thank you.